1. Field of the Invention
The present invention relates to a leak detector for detecting a leak or an extravasation of a liquid injected into a blood vessel near the surface of a human body by a syringe, and more particularly, to a leak detector for detecting a leak of a liquid injected by a liquid injector.
2. Description of the Related Art
Medical facilities currently used for imaging tomographic images of a patient include a CT (Computer Tomography) scanner, an MRI (Magnetic Resonance Imaging) apparatus, a PET (Positron Emission Tomography) apparatus, an ultrasonic diagnostic apparatus, and so on, and medical facilities currently used for imaging an angiogram of a patient include an angio apparatus, an MRA (MR Angio) apparatus, and so on. When a medical apparatus as listed above is used, a liquid such as a contrast medium, a balanced saline solution, and the like may be injected into a patient. A liquid injector has also been brought into practical use for automatically injecting a liquid. For example, the liquid injector employs a liquid syringe that is removably mounted, the liquid syringe comprises a cylinder member and a piston member slidably inserted in the cylinder member. The liquid injector has a syringe driving mechanism which presses the piston member into the cylinder member. The cylinder member, which is filled with a liquid, is coupled to a blood vessel near the surface of a human body through an extension tube and a needle, so that that the liquid in the liquid syringe is force-fed into the blood vessel of the human body by the liquid injector.
However, such a liquid injector automatically injects a liquid at a high pressure, so that even if the needle accidentally becomes detached from the blood vessel, for example, causing the liquid to leak under the skin, it is difficult for the operator to immediately recognize the leak.
To solve the problem as mentioned above, a variety of leak detectors have been proposed for detecting a leak or an extravasation of a liquid injected through a needle into a blood vessel of a human body, as described, for example, in U.S. Pat. Nos. 6,408,204, 5,964,703, 5,947,910, 6,375,624, 5,954,668, 5,334,141, 4,647,281, and 4,877,034. U.S. Pat. Nos. 6,408,204, 5,964,703, 5,947,910 disclose leak detectors for detecting a leaking liquid from a change in impedance on the surface of a human body; U.S. Pat. Nos. 6,375,624, 5,954,668, 5,334,141, 4,647,281 disclose leak detectors for detecting a leaking liquid from a change in temperature of a human organ; and U.S. Pat. No. 4,877,034 discloses a leak detector for detecting a leaking liquid from a change in optical characteristics of a blood.
However, all of these leak detectors have disadvantages of the need for a special sensor, a complicated structure, and a significant degradation in detection accuracy caused by disturbance.